I don't think you will gain from increased rgidity, because you need more rigidity to raise a heavy bed than you need to raise the carriages and effector.
I presume you are keeping the towers out of the chamber to protect the belts. You will still somehow need to have the connection between the carriages and towers crossing the chamber boundary over quite a long range of movement. Is it really that much harder to increase the movement range to the full range needed for a conventional delta?